The Crusade's a good one (if unintentionally funny in places, especially if you've read certain Persian-themed fics) - Camfield's direction is great, the script is very respectful to the culture (making a good stab at correct pronunciations for the Arab characters), and Julian Glover and Jean Marsh make immediate great impressions.
One of the early masterpieces, and it's a damn crime that two of the episodes don't exist any more. (And that the CD that came with the VHS version has no linking narration for the visual bits.)
The Space Museum - somewhat dull, but that's mainly down to Jeremy Bulloch and pals being rubbish, and Richard Shaw being pretty bad. There are some good times to be had though- the first episode sets up a good mystery (also note the Doctor admitting he actually doesn't really *get* the time-wimey part of running a time machine!), and the Doctor gets to be pretty cool in places - even if one of them's off-screen! It's also fun to note that the "what should we do to avoid our future" discussion is repeated practically verbatim in about a hundred Star Trek episodes... But this is the original!